1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to a mobile communication system employing a High Speed Downlink Packet Access (HSDPA) and a method for improving the data processing speed in the same.
2. Description of the Related Art
High Speed Downlink Packet Access (HSDPA) is a generic term used to describe the control channels associated with High Speed-Downlink Shared Channels (HS-DSCHs) for supporting high speed downlink packet transmission in wideband code divisional multiple access (W-CDMA) communication systems, and devices, systems and methods using the channels. A Hybrid Automatic Retransmission reQuest (HARQ) method has been proposed to support the HSDPA. The HARQ method and the structure of a conventional W-CDMA communication system will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing the structure of the conventional W-CDMA communication system.
The W-CDMA communication system includes a Core Network (CN) 100, a plurality of Radio Network Subsystems (RNS) 110 and 120 and User Equipment (UE) 130. Each of the RNSs 110 and 120 includes a Radio Network Controller (RNC) and a plurality of Node Bs (also referred to as base stations or cells). For example, the RNS 110 includes an RNC 111 and a plurality of Node Bs 113 and 115. RNCs are classified into a Serving RNC (SRNC), a Drift RNC (DRNC) or a Controlling RNC (CRNC) according to their roles. Specifically, the SNRC and the DRNC are classified according to the services they provide to the UE. That is, an RNC, which manages information of a UE and handles data communication between the UE and the core network, is referred to as an SRNC of the UE. When data of a UE is transmitted to and received from the SRNC of the UE via a different RNC, the different RNC is referred to as a DRNC of the UE. An RNC for controlling Node Bs is referred to as a CRNC of the Node Bs. In the example of FIG. 1, if the RNC 111 manages information of the UE 130, the RNC 111 is an SRNC of the UE 130, and if the UE 130 moves and communicates its data via the RNC 112, the RNC 112 is a DRNC of the UE 130. The RNC 111, which controls the Node B 113, is a CRNC of the Node B 113.
A description will now be given of the HARQ method, particularly the n-channel Stop And Wait Hybrid Automatic Retransmission reQuest (SAW HARQ) method. A general ARQ method is based on exchange of acknowledgement (ACK) and retransmission packet data between a UE and an RNC. To increase the transmission efficiency of the ARQ method, the HARQ method employs the Forward Error Correction (FEC) technique. In the HSDPA, an ACK and retransmission packet data are exchanged between the UE and the Node B. The HSDPA introduces the n-channel SAW HARQ method in which N processes are provided so that even when a specific process at a transmitting side has not received an ACK to its transmission, the packet data can be transmitted through other processes set in the transmitting side. The Stop And Wait Automatic Retransmission reQuest (SAW ARQ) method transmits the next packet data only after receiving an ACK to previously transmitted packet data. As a result, the SAW ARQ method has low channel utilization. The n-channel SAW HARQ method can increase the channel utilization by allowing the other processes to consecutively transmit other packet data without receiving an ACK to the previous packet data. Specifically, in the n-channel SAW HARQ method, N processes are set between the UE and the Node B, and the transmitting side also transmits process identifiers allowing the receiving side to identify each process. Thus, the UE, which has received a plurality of packet data, can identify a process through which each of the plurality of packet data was transmitted so that the UE can afterwards perform operations corresponding to the identified process.
The layer architecture of the W-CDMA system employing the HSDPA described above requires an additional function for the HARQ in the Medium Access Control (MAC) layer. In order to satisfy this requirement, the layer architecture of the W-CDMA system employing the HSDPA has been modified from the conventional layer architecture of the W-CDMA system that does not employ the HSDPA. Specifically, the layer architecture of the W-CDMA system employing the HSDPA has implemented a Medium Access Control-high speed (MAC-hs) entity to support the HSDPA, in addition to the Medium Access Control—(MAC-c/sh) (“control/shared”) and Medium Access Control—(MAC-d) (“dedicated”) entities in the MAC layer architecture of the conventional W-CDMA communication system.
The MAC-hs entity primarily provides functions for the HARQ on the High Speed-Downlink Stored Channel (HS-DSCH) to support the HSDPA. If no error is detected in a data block (i.e. packet data) received from a wireless channel, the MAC-hs entity transmits the ACK to the Node B. If an error is detected in the data block, the MAC-hs entity produces a Non ACKnowledgement (NACK) requesting retransmission of the data block and transmits the produced NACK to the Node B.
The MAC layer provides a service referred to as the “unacknowledged transfer of MAC SDU” to the upper layer. In this service, the MAC layer receives MAC Protocol Data Unit(s) (PDU(s)) from a physical layer (PHY) as its lower layer, and processes the received MAC PDU(s) to produce a MAC Service Data Unit(s) (SDU(s)), and then transfers the MAC SDU(s) (i.e. Radio Link Control (RLC) PDU(s)) in a suitable manner to the RLC layer as its upper layer. This description of the service takes into account only the downlink of the UE since the HSDPA service is associated with downlink in the present invention.
Channels used in the HSDPA communication system can be divided into downlink (DL) and uplink (UL) channels. Some examples of the downlink channel are a High Speed-Shared Control channel (HS-SCCH), an associated Dedicated Physical Channel (DPCH) and a High Speed-Physical Downlink Shared Channel (HS-PDSCH), and an example of the uplink channel is a High Speed Dedicated Physical Control Channel (HS-DPCCH).
The HS-PDSCH is a physical channel supporting user traffic for HSDPA services, and the HS-DSCH is a transport channel (i.e. a channel for transferring MAC-PDU(s) between the PHY and the MAC layers) mapped to the physical channel. Actual user data carried through the HS-DSCH is referred to as a Medium Access Control-high speed Protocol Data Unit (MAC-hs PDU). The structure of the MAC-hs PDU will now be described with reference to FIG. 2.
FIG. 2 is a drawing showing the structure of a MAC-hs PDU carried through the HS-DSCH.
As shown in FIG. 2, the MAC-hs PDU includes a MAC-hs header field 210, a MAC-hs Service Data Unit (SDU) field 220 and a padding field 230. The MAC-hs header 210 includes various fields as follows.
(1) Version Flag (VF): a one-bit flag indicating the version of a communication system.
(2) Queue ID: a 3-bit field providing for the identification of a priority queue of the MAC-hs PDU 200. That is, the Queue ID is an identification of a reordering queue managed by the UE to support the HSDPA.
(3) Transmission Sequence Number (TSN): a 6-bit sequence number indicating the sequence of the transmission of the MAC-hs PDUs in the priority queue.
(4) SID_x: a 3-bit field indicating the size of the MAC-dedicated (MAC-d) PDUs belonging to the x-th set of concatenated MAC-d PDUs of the same size included in a MAC-hs PDU.
(5) N_x: a 7-bit field indicating the number of the MAC-d PDUs belonging to the x-th set of concatenated MAC-d PDUs of the same size.
(6) F (Flag): a one-bit flag indicating if the F field is the end of the current MAC-hs header. If the flag value is set to “1”, it indicates that the F field is the end of the current MAC-hs header, followed by a MAC-hs SDU, and if the flag value is set to “0”, it indicates that the F field is followed by an SID field.
As shown in FIG. 2, one MAC-hs PDU 200 may include a plurality of MAC-hs SDUs 220. That is, the MAC-hs payload includes a plurality of MC-hs SDUs. The padding field 230 is added to the MAC-hs PDU 200 when the sum of the sizes of the MAC-hs payload and header is less than a transport block set size (i.e. the size of a transport block set transferred to an associated HS-SCCH).
In FIG. 2, the MAC-hs SDU 220 is transferred to the MAC-d entity so that the MAC-d header is removed, and is then transferred as the MAC-d SDU(s) (i.e. RLC PDU(s)) to the upper RLC layer. The MAC-hs SDU is the same as the MAC-d PDU. As shown in FIG. 2, each MAC-hs PDU includes a MAC-hs header of at least 21 bits as expressed by Equation 1.Length of MAC-hs header=10+11P (P=1, 2, 3 . . . )   (1)where P is the number of sets of SID, N and F fields.
The MAC-d PDU, which is the MAC-hs SDU, is configured as shown in FIG. 3.
FIG. 3 is a diagram showing the configuration of each MAC-d PDU mapped to an HS-DSCH.
As shown in FIG. 3, each MAC-d PDU 220 includes a C/T field 221 and a MAC SDU 222. The C/T field 221 is used as identification of a logical channel transmitted through the HS-DSCH. The logical channel is used to allow the MAC layer to provide a data transfer service to the RLC layer as its upper layer. Each C/T field 221 is composed of 4 bits and can identify up to 15 logical channels. One logical channel is generally allocated to one radio bearer, but a plurality of logical channels may also be used to set one radio bearer as circumstances permit. Thus, the C/T field 221 can be used as an identification for each logical channel, and the MAC SDU 220 is transferred to the upper layer through the identification process.
In FIG. 3, the 4-bit C/T field in each MAC-d PDU may be present or not depending on whether or not multiplexing on the MAC is performed. Since the HSDPA does not operate in TM (Transparent Mode) RLC mode due to the ciphering, the size of the MAC SDU (i.e. an RLC PDU) in FIG. 3 is a multiple of 8 bits. The size of each MAC-d PDU (MAC-hs SDU) can be expressed by Equation 2.Length of MAC-d PDU=8M+4K   (2)(M=1, 2, . . . . integer; and K is 0 or 1)
In the HSDPA, the MAC layer processes a MAC-hs PDU received from the physical layer to produce RLC PDU(s) (i.e. MAC-d SDU(s)) and transfers the produced MAC-d SDU(s) to the upper RLC layer.
In most cases, the length of the MAC-hs header of the MAC-hs PDU received through the HS-PDSCH is not a multiple of 8 bits. The MAC-hs PDU is composed of a bit stream of a consecutive MAC-hs header and payload.
Due to the structure of the MAC-hs PDU, bit operations such as bit masking, bit stream coping and bit shifting, which lower the processing speed of the HSDPA service, must be implemented when the MAC layer in the UE system processes and converts the MAC-hs PDU to MAC-d PDU(s) and also when the RLC layer processes the RLC PDU(s) extracted from the MAC-hs PDU to produce the RLC SDU(s).
Even when the MAC-d PDUs transferred through a MAC-hs PDU are a multiple of 8 bits (i.e. even when no multiplexing on MAC is performed), if the MAC-hs header is not a multiple of 8 bits, the MAC-hs header and the MAC-d PDU(s) are composed of a data stream of consecutive bits, so that bit operations, which may decrease the data transfer rate, are required when the MAC layer processes and transfers such a data stream to the RLC layer and also when the RLC layer forms the RLC SDU(s).